NERVOUS SYSTEM OF THE VERTEBRATA. 433 



The figure which Gotte gives to prove this does not appear to me fully to 

 bear out his conclusion ; which if true is very important. Although I 

 directed my attention specially to this point, I could find no indication in 

 Elasmobranchii of a process similar to that described by Gotte, and his 

 observations have not as yet been confirmed for other Vertebrates. Gotte 

 compares the pineal gland to the long-persisting pore which leads into the 

 cavity of the brain in the embryo of Amphioxus, and we might add the 

 Ascidians, and, should his facts be confirmed, the conclusion he draws from 

 them would appear to be well founded. 



The later stages in the development of the pineal gland in 

 different Vertebrates have not in all cases been fully worked 

 out 1 . 



In Elasmobranchii the pineal gland becomes in time very 

 long, and extends far forwards over the roof of the cerebral 



fruS 



FIG. 255. LONGITUDINAL VERTICAL SECTION THROUGH THE ANTERIOR PART 



OF THE BRAIN OF AN EMBRYO RABBIT OF FOUR CENTIMETRES. (After 



Mihalkovics.) 



The section passes through the median line so that the cerebral hemispheres are 

 not cut ; their position is however indicated in outline. 



spt. septum lucidum formed by the coalescence of the inner walls of part of the 

 cerebral hemispheres; cna. anterior commissure; frx. vertical pillars of the fornix; 

 cal. genu of corpus callosum; tnn. lamina terminalis; hins. cerebral hemispheres; 

 olf. olfactory lobes ; ad. artery of corpus callosum ; fmr. position of foramen of 

 Munro; chd$. choroid plexus of third ventricle ; pin. pineal gland; cmp. posterior 

 commissure; bgm. lamina uniting the lobes of the mid-brain; chm. optic chiasma ; 

 hpli. pituitary body ; inf. infundibulum ; pns. pons Varolii ; pde. cerebral peduncles ; 

 agd. iter. 



1 For a full account of this subject vide Ehlers (No. 337). 

 B. Til. 28 



